HEATING BY HOT WATER. 
201 
and usually made in either copper or tin, is so ruinously 
extravagant in fuel as to be totally out of the question, 
fully three-fourths, if not a still 
larger proportion, of the heat 
generated by the (atmospheric) gas 
burner passing directly away by the 
flue-pipe and being wasted. Some 
of the newer forms extensively 
advertised are but little better than 
the above, but others again afford 
a) 
W000 0 OV OVD 
Fig. 138, 
vastly better results, and consume but little gas or oil in 
proportion to the work done. Some of the tubular forms 
Fic. 139. 
are very good, those 
fitted with a number 
of horizontal tubes 
being much more 
economical than such 
as have vertical tubes 
only, though these are 
immensely superior to 
the old conical boiler. 
These tubular boilers 
on a small scale are 
however somewhat 
costly, and require 
frequent cleaning also. 
On the whole, de- 
cidedly the most simple 
and at the same time 
generally effective 
apparatus of this kind 
